Hello
=20
I'm a student in computer science in Belgium and it is my last year of st=
udy.=20
My thesis consists in realising an automatic horizon for a camera which
is in a remotily controled helicopter (www.flying-cam.com).
=20
I studied Intel assembly at school, but I've never learned how to
program a microcontroler. So I looked for help and tutorials on the
Internet. I'm working with PIC's since only two months.

I'm currently coding my automatic horizon software on a PIC16F877
and I have some real time problems. I'll try explain that clearly.

My PIC must measure a PWM signal in input, then it computes this value=20
with values from captors (accelerometer and gyro), finaly it outputs the
result in the form of an other PWM signal.=20
=20
I must measure the input signal with 1 =B5s precision.
I use the RBIF interrupt to detect the edges of the input signal,=20
timer 0 to measure the lenght of the signal. I use timer 1 with the CPP=20
to output the result signal.
TMR2 is used to generate the frequency of the output
signal. The problem is that RBI interrupt can occur while=20
executing the tmr2 interrupt code, and the measure of
the input signal will be faulty because the RBI does not
react immediately. So I've used nested=20
interrupts with a software stack (I found this method in the piclist
source code library), but there is always a
part of the code where interrupts are disabled.
=20
Does anybody has an idea to make this measure accurately ?

Thanks a lot for your help.


Laurent

NB : I'm french speaking, so I hope I haven't made too
much mistakes in English

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